In order to drive a travelling machine such as a scooter, a snowmobile, a buggy car or the like which makes much of simplicity, there has been used a small-sized two cycle internal combustion engine as a drive power and a centrifugal clutch type continuously variable transmission as a transmission to transmit an output power of the internal combustion engine to drive wheels of the travelling machine. Many travelling machines have no reverse gear assembled in the continuously variable transmission from a requirement of important items of small-size, lightness and inexpensiveness.
Since vehicles having no reverse gear assembled in the transmission cannot move in a backward direction, they have to change their direction by lifting the whole vehicles when their travelling direction should be reversed, which causes them to have a poor manipulation.
In order to enable reversion of the travelling direction of the travelling machine having no reverse gear provided therein, the rotative direction of the internal combustion engine has to be reversed, as required.
The two cycle internal combustion engine can rotate in both of forward and reverse directions and can be normally driven either in the forward direction and in the reverse direction.
More particularly, as an ignition position (an angular position of a rotary shaft of the two cycle internal combustion engine as it is ignited) of the engine is advanced to an over spark advance position (a position further advancing beyond the optimum maximum spark advance position on its normal operation), a piston moving toward a top dead center thereof is forced back far away from the top dead center so that the rotative direction of the engine is reversed. After the reversion of the rotative direction of the engine is checked, the ignition position is returned to the optimum ignition position where the rotative direction of the engine reverse to the former direction can be maintained. Thus, the two cycle internal combustion engine can continue to rotate in the condition in which the rotative direction is reversed.
There has been well known a process in which the rotative direction of the two cycle internal combustion engine is reversed by controlling its reversion while the ignition position of the engine is advanced to the over spark advance position necessary for reversing the rotative direction of the engine when a reversion instruction is given instructing the reversion of the engine.
FIG. 9 illustrates an algorithm of interruption routine which is conducted by a microcomputer as a reversion instruction is generated by a driver when a rotative direction instruction switch is operated in a prior art process for controlling the change-over of the rotative direction of the engine.
With this algorithm followed, when the reversion instruction is given, a step 1 of FIG. 9 is conducted wherein it is confirmed whether the rotative direction of the engine being now driven is identical to that instructed by the driver.
As a result of the confirmation of the step 1, when it is confirmed that the rotative direction of the engine being now driven is not identical to that instructed by the driver, the process is moved to a step 2 of FIG. 9 wherein the reversion control is made. In this reversion control, the ignition position of the engine is advanced to the over spark advance position necessary for reversing the rotative direction of the engine and the over spark advance condition of the ignition position is maintained until the reversion of the rotative direction of the engine is confirmed.
In the reversion control of the step 2, as the reversion of the rotative direction of the engine is confirmed, the process is moved to a step 3 of FIG. 9 wherein the ignition control is moved to the normal ignition position while the rotative direction is maintained in the reverse condition. Thus, the engine continues to be driven in the condition of reversion of the rotative direction of the engine.
With the algorithm of FIG. 9 followed, if the driver unintentionally operates the rotative direction instruction switch during travelling, or if a reversion instruction generator means such as a rotative direction instruction switch breaks down, then the travelling machine will quickly move back because the engine abruptly rotates in the reverse direction.
If the throttle valve is in the state of being opened even though the travelling machine is at a stop when the driver operates the rotative direction instruction switch, the travelling machine will disadvantageously travel in an abrupt manner because the engine is quickly accelerated as soon as the rotative direction of the engine is reversed.
These undesirable conditions should be avoided in order to make a practical use of the travelling machine having a system of reversing its travelling direction by reversing the rotative direction of the engine mounted thereon.